There are cases where light is emitted from a substance at a low temperature at which the substance can not emit any visible ray by thermal radiation. Such lighting phenomenon is referred to as luminescence. Luminescence means the emission of light having a wavelength which correspond to the energy difference when a substance is converted to a stable state having low energy from an unstable state having high energy. Thus, in order to make a substance emit such light, it is necessary to make the substance to an unstable excited state having high energy. Various sources of energy such as light, chemical reactions, heat, electricity, cathode-emitted electron or the like may be used. Said difference sources of energy produce different types of light emission such as photo-, chemi-, thermo-, electro-, cathodo-luminecence, or the like.
Luminescence can be classified as fluorescence and phosphorescence. Fluorescence refers to the phenomenon that a substance emits light only when the substance is irradiated, and phosphorescence refers to the phenomenon that a substance continuously emits a light even after the irradiation to the substance is ended.
In this regard, a substance emitting fluorescence is referred to as a fluorescent element or a fluorescent substance. Such fluorescent substance can be divided into a single-photon absorption fluorescent substance which absorbs only one photon under a strong laser to emit the fluorescence and a multi-photon absorption fluorescent substance which absorbs a plurality of photons to emits the fluorescence. The present invention relates to a new water-soluble fluorescent compound simultaneously having a single-photon absorption fluorescent feature as well as a multi-photon absorption fluorescent feature, in particular, 2-photon absorption fluorescent feature.
In more particular, the present invention was completed by finding a new water-soluble fluorescent compound of (E)-4-(8-hydroxy-6-(((2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yl)oxy)naphthalen-2-yl)but-3-en-2-one (hereinafter, referred to as resveratrone 6-O-β-glucoside or resveratrone glucoside) having a high single-photon absorptive efficiency and/or 2-photon absorptive efficiency after a photochemical reaction of a conventionally known glycosylated derivative of resveratrol, for example, polydatin (hereinafter, referred to as resveratrol 3-O-β-glucoside or resveratrol glucoside) which is frequently found in peanuts, grapes, berries and the like.